[Abstract Title]. - Society for Neuroscience

Program#/Poster#: 275.17/JJ32
Topic: D.16.d. Kinematics and Muscle Activity
Support: NIH K01 HD050369
ISB Predoctoral Award
Title: Impaired postural adjustments to a predictable perturbation during step initiation in the
elderly
Authors: *S.-C. TSENG 1 , S. J. STANHOPE 3,4 , S. M. MORTON 1,2 ;
1 Phys Ther & Rehab Sci., 2 Anat. & Neurobio., Univ. of Maryland Sch. of Med., Baltimore, MD;
3 Health, Nutr. & Exercise Sci., Univ. of Delaware, Newark, DE; 4 Mechanical Engin., Univ. of
Delaware, Newark, DE
Abstract: Prior to and during gait, postural adjustments counteract the resultant forces induced
by self-movement, offset unexpected perturbations, and correct movement errors, thereby
minimizing postural instability and preventing falls. Here, we investigated acquisition of postural
adjustments by healthy elderly subjects in response to a novel but predictable perturbation during
a visually-guided step. We recorded 3D kinematics and ground reaction forces from 18 healthy
elderly adults and an equal number of young controls. Subjects performed, as quickly and
accurately as possible, a reactive, visually-guided stepping movement with the right foot toward
an illuminated target located on the floor. During a block of baseline trials, the target appeared
directly in front the stepping leg, at a distance of 40% of body height. During a block of
perturbation trials, the target first appeared in the baseline position but was replaced,
instantaneously during mid-step, by a second target that was shifted either toward the right or the
left of the baseline location by a distance of 10% of body height. Subjects were randomly
assigned to perform the perturbation block with either rightward- or leftward-shifting targets. To
measure the acquisition of altered postural adjustments, we quantified changes in several
variables over the duration of the perturbation block: the durations of three movement phases,
the timing and magnitudes of foot path modifications, and the timing and magnitudes of force
modifications. These variables were compared over three key time periods: initially, early, and
late in the perturbation block. We found that the young group was able to quickly alter their
stepping in response to the predictable perturbation, completely adjusting their performance by
the end of the early perturbation period. In contrast, the elderly group required additional
practice; they were unable to adjust lateral propulsive forces, shorten foot path modification
times, and stabilize several other temporal variables by the end of the early perturbation period.
By the late perturbation period, however, the elderly performed similarly to the young group on
most measures. We also found that stepping accuracy showed direction-specific effects in both
groups, probably because of an increase in the challenge to medial-lateral postural stability in the
leftward step. Our results indicate that during step initiation, elderly subjects have a slowed but
intact ability to adjust postural responses to a predictable perturbation. The findings suggest that
elderly subjects may have impaired mechanisms for correcting postural adjustments using trialand-error
practice.